Reading module and image reading device and image forming apparatus therewith

ABSTRACT

A reading module has a light source, an optical system, and a sensor. The optical system images, as image light, reflected light of light radiated from the light source to a document. In the sensor, the image light imaged by the optical system is converted into an electrical signal. The optical system has a mirror array and an aperture stop portion. In the mirror array, reflection mirrors are coupled together in an array in the main scanning direction. The aperture stop portion has a first aperture adjusting the amount of the image light reflected from a reflection mirror and a second aperture shielding stray light entering the first aperture from an adjacent reflection mirror. Between the first and second apertures, a reflection reduction mechanism is provided that reduces reflection, toward the first aperture, of light other than the image light traveling from the second to first aperture.

INCORPORATION BY REFERENCE

This application is based upon and claims the benefit of priority fromthe corresponding Japanese Patent Application No. 2016-232312 filed onNov. 30, 2016 and Japanese Patent Application No. 2017-143699 filed onJul. 25, 2017, the entire contents of both of which are incorporatedherein by reference.

BACKGROUND

The present disclosure relates to a reading module that is incorporatedin digital copiers, image scanners, and the like and that readsreflected image light of the light radiated to a document, and to animage reading device and an image forming apparatus incorporating such areading module.

Conventional optical imaging systems for image reading devicesincorporated in multifunction peripherals and the like adopting anelectro-photographic process include a reduction optical system whereimages are formed on a reduced scale and a unity magnification opticalsystem where images are formed at unity magnification without beingreduced.

In the reduction optical system, a reduced image is formed on an imagesensor whose size is smaller than that of a document by use of aplurality of plane mirrors and an optical lens, and then the image isread. In the reduction optical system, as an image sensor, acharge-coupled device called a CCD sensor is used. The reduction opticalsystem advantageously has a deep depth of field. Here, the depth offield is the range in which, even when a subject (here a document) isdisplaced in the direction of the optical axis from the in-focusposition, the subject can be seen as if in focus. This means that, witha deep depth of field, even when the document is displaced from thepredetermined position, it is possible to obtain a satisfactory image.

On the other hand, the reduction optical system inconveniently has avery large optical path length (the distance light travels from asubject to the sensor) of 200 to 500 mm. In image reading devices, forthe purpose of securing the optical path length in a limited space in acarriage, the direction in which light travels is changed by use of aplurality of plane mirrors. This increases the number of componentsrequired, leading to an increased cost. When a lens is used in theoptical system, chromatic aberration occurs due to variation in therefractive index with wavelength. To correct the chromatic aberration, aplurality of lenses are required. As will be seen from the above, usinga plurality of lenses becomes one of the factors that increase the cost.

In the unity magnification optical system, an image is read by beingimaged, with a plurality of erect-image rod-lenses with unitymagnification arranged in an array, on an image sensor whose size issimilar to that of a document. In the unity magnification opticalsystem, as an image sensor, a photoelectric conversion device calledCMOS (complementary MOS) sensor is used. The unity magnification opticalsystem advantageously has the following advantages. A smaller opticalpath length of 10 to 20 mm compared with the reduction optical systemhelps achieve compactness. Imaging by use of rod lenses alone eliminatesthe need for mirrors required in the reduction optical system. Thishelps make a scanner unit that incorporates a unity magnificationoptical system sensor slim. The simple construction helps achieve costreduction. On the other hand, the unity magnification optical system hasa very small depth of field, and thus when a document is displaced inthe direction of the optical axis from a predetermined position, asevere blur results from image bleeding due to different magnificationsof the individual lenses. As a result, it is inconveniently impossibleto uniformly read a book document or a document with an uneven surface.

In recent years, a method has been proposed in which, instead of thereduction magnification optical system or the unity magnificationoptical system described above, an image is read by use of a reflectionmirror array in the imaging optical system. In this method, a pluralityof reflection mirrors are arranged in an array, and a document read indifferent reading regions corresponding to the reflection mirrors on aregion-by-region basis is formed into an inverted image on a reducedscale on a sensor. Unlike in the unity magnification optical system thatuses a rod-lens array, one region is read and imaged with one opticalsystem. By adopting the telecentric optical system as the imagingsystem, when a document is read on a region-to region basis, no imagebleeding occurs as a result of images with different magnificationsoverlapping with each other; it is thus possible to suppress imageblurring and achieve a compound-eye reading method.

In this method, the optical system uses mirrors alone, and thus unlikein a case where the optical system uses a lens, no chromatic aberrationoccurs. This makes it unnecessary to correct chromatic aberration, andthus helps reduce the number of elements constituting the opticalsystem.

SUMMARY

According to a first aspect of the present disclosure, a reading moduleincludes a light source, an optical system, and a sensor. The lightsource radiates light to a document. The optical system images, as imagelight, reflected light of the light radiated from the light source tothe document. In the sensor, a plurality of imaging regions forconverting the image light imaged by the optical system into anelectrical signal are arranged next to each other in the main scanningdirection. The optical system includes a mirror array and a plurality ofaperture stop portions. In the mirror array, a plurality of reflectionmirrors whose reflection surfaces are aspherical concave surfaces arecoupled together in an array in the main scanning direction. Theaperture stop portions are each provided in the optical path of imagelight between a reflection mirror and an imaging region, and theaperture stop portions each have a first aperture which adjusts theamount of image light reflected from the reflection mirror and a secondaperture which is formed on the mirror array side of the first aperture,the second aperture shielding stray light that strikes the firstaperture from an adjacent reflection mirror. Between the first apertureand the second aperture, a reflection reduction mechanism is providedthat reduces reflection, toward the first aperture, of light other thanthe image light traveling from the second aperture to the firstaperture.

Further features and advantages of the present disclosure will becomeapparent from the description of embodiments given below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side sectional view showing the overall construction of animage forming apparatus 100 incorporating an image reading portion 6that uses a reading module 50 according to the present disclosure;

FIG. 2 is a side sectional view showing the internal structure of thereading module 50 according to a first embodiment of the presentdisclosure incorporated in the image reading portion 6;

FIG. 3 is a partial perspective view showing the internal structure ofthe reading module 50 according to the first embodiment;

FIG. 4 is a sectional plan view showing the configuration between anoptical unit 40 and a sensor 41 in the reading module 50 according tothe first embodiment;

FIG. 5 is a partly enlarged view showing the optical path between thereflection mirrors 35 a and 35 b and the sensor 41 in FIG. 4;

FIG. 6 is a partly enlarged view showing the optical path between thereflection mirror 35 a and an imaging region 41 a on the sensor 41,showing a configuration where light shielding walls 43 are provided atthe boundaries of the imaging region 41 a;

FIG. 7 is a partial perspective view showing the structure of theoptical unit 40 in the reading module 50 according to the firstembodiment;

FIG. 8 is a perspective view of an aperture stop portion 37 used in thereading module 50 according to the first embodiment as seen from theturning mirror 34 side;

FIG. 9 is a perspective view of the aperture stop portion 37 used in thereading module 50 according to the first embodiment as seen from thesensor 41 side;

FIG. 10 is a perspective view of the aperture stop portion 37 used inthe reading module 50 according to the first embodiment as seen fromabove;

FIG. 11 is a diagram schematically showing how stray light F enters theaperture stop portion 37 used in the reading module 50 according to thefirst embodiment;

FIG. 12 is a perspective view of an aperture stop portion 37 used in areading module 50 according to a second embodiment of the presentdisclosure as seen from above;

FIG. 13 is a diagram schematically showing how stray light F enters theaperture stop portion 37 used in the reading module 50 according to thesecond embodiment;

FIG. 14 is a sectional plan view showing the structure between onereflection mirror 35 b and the sensor 41 in the reading module 50according to the second embodiment;

FIG. 15 is perspective view of an aperture stop portion 37 used in areading module 50 according to a third embodiment of the presentdisclosure as seen from the turning mirror 34 side;

FIG. 16 is an enlarged view of the aperture stop portion 37 according tothe third embodiment as seen from the second aperture 37 b side;

FIG. 17 is a perspective view of an aperture stop portion 37 used in areading module 50 according to a fourth embodiment of the presentdisclosure as seen from the turning mirror 34 side;

FIG. 18 is a perspective view of the aperture stop portion 37 used inthe reading module 50 according to the fourth embodiment of the presentdisclosure as seen from the sensor 41 side;

FIG. 19 is a sectional view along line 200-200 in FIG. 17;

FIG. 20 is a diagram schematically showing how light is reflected on aninner surface 37 e of a second aperture 37 b in the aperture stopportion 37 used in the reading module 50 according to the fourthembodiment of the present disclosure; and

FIG. 21 is a partial sectional view showing a modified example of thereading module 50 according to the present disclosure, showing aconfiguration where image light d is reflected three times on a turningmirror 34.

DETAILED DESCRIPTION

Hereinafter, embodiments of the present disclosure will be describedwith reference to the accompanying drawings. FIG. 1 is a diagram showingan outline of the construction of an image forming apparatus 100incorporating an image reading portion 6 that uses a reading module 50according to the present disclosure. In the image forming apparatus 100shown in FIG. 1 (here a digital multifunction peripheral is taken as anexample), a copy operation proceeds as follows. In the image readingportion 6, which will be described later, document image data is readand is converted into an image signal. On the other hand, in an imageforming portion 3 in a multifunction peripheral main body 2, aphotosensitive drum 5 that rotates in the clockwise direction in FIG. 1is electrostatically charged uniformly by a charging unit 4. Then, by alaser beam from an exposure unit (such as a laser scanner unit) 7, anelectrostatic latent image is formed on the photosensitive drum 5 basedon the document image data read in the image reading portion 6. Then,developer (hereinafter, referred to as toner) is attached to the formedelectrostatic latent image by a developing unit 8, and thereby a tonerimage is formed. Toner is fed to the developing unit 8 from a tonercontainer 9.

Toward the photosensitive drum 5 having the toner image formed on it asdescribed above, a sheet is conveyed from a sheet feeding mechanism 10via a sheet conveyance passage 11 and a registration roller pair 12 tothe image forming portion 3. The sheet feeding mechanism 10 includessheet feed cassettes 10 a and 10 b and a stack bypass (manual feed tray)10 c arranged over the sheet feed cassettes 10 a and 10 b. When theconveyed sheet passes through a nip between the photosensitive drum 5and a transfer roller 13 (image transfer portion), the toner image onthe surface of the photosensitive drum 5 is transferred to the sheet.Then, the sheet having the toner image transferred to it is separatedfrom the photosensitive drum 5, and is conveyed to a fixing portion 14,which has a fixing roller pair 14 a, so that the toner image is fixedthere. The sheet having passed through the fixing portion 14 isdistributed among different conveyance directions by passage switchingmechanisms 21 and 22 arranged at branch points in a sheet conveyancepassage 15. The sheet is then, as it is (or after being conveyed to areverse conveyance passage 16 and being subjected to two-sided copying),discharged onto a sheet discharge portion composed of a first dischargetray 17 a and a second discharge tray 17 b.

After toner image transfer, toner left unused on the surface of thephotosensitive drum 5 is removed by a cleaning device 18. Electriccharge remaining on the surface of the photosensitive drum 5 is removedby a destaticizer (unillustrated) arranged on the downstream side of thecleaning device 18 in the rotation direction of the photosensitive drum5.

In an upper part of the multifunction peripheral main body 2, the imagereading portion 6 is arranged, and a platen (document presser) 24 isopenably/closably provided that presses and thereby holds a documentplaced on a contact glass 25 (see FIG. 2) of the image reading portion6. On the platen 24, a document conveyance device 27 is provided.

In the multifunction peripheral main body 2, a control portion (CPU) 90is arranged that controls the operation of the image forming portion 3,the image reading portion 6, the document conveyance device 27, and thelike.

FIG. 2 is a side sectional view showing the internal structure of areading module 50 according to a first embodiment of the presentdisclosure incorporated in the image reading portion 6. FIG. 3 is aperspective view of the reading module 50 according to this embodiment,showing the optical path from a document 60 to a sensor 41. FIG. 4 is asectional plan view showing the configuration between an optical unit 40and the sensor 41 in the reading module 50 according to this embodiment.Although a mirror array 35 constituting the optical unit 40 shown inFIG. 4 reflects rays of light, for the sake of convenience ofdescription, FIG. 4 shows a model where the optical unit 40 transmitsrays of light.

The reading module 50 reads an image on the obverse side (lower side inFIG. 2) of the document 60 placed on the contact glass 25 while movingin the sub-scanning direction (the direction indicated by arrows A andA′). The reading module 50 also reads an image on the obverse side ofthe document 60 conveyed by the document conveyance device 27 (seeFIG. 1) while remaining at rest right under the automatic readingposition of the contact glass 25.

As shown in FIG. 2, the reading module 50 includes, in a housing 30thereof, a light source 31, a plane mirror 33 a, a turning mirror 34, amirror array 35 composed of a plurality of reflection mirrors whosereflection surfaces are aspherical concave surfaces, an aperture stopportion 37, and a sensor 41 as a reading means. The sensor 41 issupported on a sensor substrate 42 (see FIG. 4). As the sensor 41, a CCDor CMOS image sensor is used according to the design. The reading module50 has a home position right under a shading plate (unillustrated) foracquiring white reference data.

With this configuration, to read a document image in a fixed-documentmanner, image reading proceeds as follows. First, a document 60 isplaced on the contact glass 25 with the image side down. Then, while theimage side of the document 60 is irradiated with light emitted from thelight source 31 and transmitted through an opening 30 a the readingmodule 50 is moved at a predetermined speed from the scanner home sideto the scanner return side. As a result, the light reflected from theimage side of the document 60, that is, the image light d (indicated bythe solid arrows in FIG. 2), has its optical path changed by the planemirror 33 a, and is then reflected on the turning mirror 34. Thereflected image light d is converged by the mirror array 35, isreflected again on the turning mirror 34, passes through the aperturestop portion 37, and is imaged on the sensor 41. The image light d ofthe formed image is, in the sensor 41, divided into pixels to beconverted into electrical signals commensurate with the densities ofindividual pixels.

On the other hand, to read a document image in a sheet-through manner,image reading proceeds as follows. The reading module 50 is moved toright under the image reading region (image reading position) of thecontact glass 25. Then, while the image side of a document, which isconveyed one sheet after another while being lightly pressed against theimage reading region by the document conveyance device 27, is irradiatedwith light from the light source 31, the image light d reflected fromthe image side is imaged on the sensor 41 via the plane mirror 33 a, theturning mirror 34, the mirror array 35, the turning mirror 34, and theaperture stop portion 37.

As shown in FIG. 3, the mirror array 35 and the aperture stop portion 37are integrally formed of the same material and are integrated into aunit as the optical unit 40. By integrally forming the mirror array 35and the aperture stop portion 37, it is possible to hold the position ofthe mirror array 35 relative to the aperture stop portion 37 with highaccuracy. Thereby, it is possible to effectively prevent imagingperformance from degrading as a result of the relative position varyingwith expansion or contraction of the mirror array 35 and the aperturestop portion 37 due to change in temperature.

The turning mirror 34 is arranged at a position facing the mirror array35, and reflects both rays of light (the image light d) which travelfrom the document 60 via the plane mirror 33 a to be incident on themirror array 35 and rays of light (the image light d) which arereflected from the mirror array 35 to enter the aperture stop portion37.

As shown in FIG. 4, the mirror array 35, which images the image light don the sensor 41, is composed of a plurality of reflection mirrors 35 a,35 b, 35 c . . . , which correspond to predetermined regions of thesensor 41, coupled together in an array in the main scanning direction(the direction indicated by arrows B and B′).

In the configuration according to this embodiment, the image light dreflected from reading regions Ra, Rb . . . (see FIG. 5) of the document60 separated in the main scanning direction has its optical path changedby the plane mirror 33 a and the turning mirror 34 (see FIG. 2), and isincident on the reflection mirrors 35 a, 35 b, 35 c . . . of the mirrorarray 35. The image light d is reduced at predetermined reductionmagnifications by the reflection mirrors 35 a, 35 b, 35 c . . . , isreflected again on the turning mirror 34, passes through the aperturestop portion 37, and is focused on corresponding imaging regions of thesensor 41 to form inverted images.

The inverted images formed on the imaging regions are converted intodigital signals, and thus magnification enlargement correction isperformed through data interpolation according to the reductionmagnifications for the respective imaging regions to reverse the datainto erect images. Then, the images of the imaging regions are connectedtogether to form an output image.

The aperture stop portion 37 is arranged at the focal points of thereflection mirrors 35 a, 35 b, and 35 c . . . constituting the mirrorarray 35. The physical separation distance (the distance in the up/downdirection in FIG. 2) between the aperture stop portion 37 and the mirrorarray 35 is determined according to the reduction magnification of themirror array 35. In the reading module 50 according to this embodiment,the turning mirror 34 reflects rays of light twice, and this makes itpossible to secure the optical path length from the mirror array 35 tothe aperture stop portion 37, and thus to minimize theincidence/reflection angle of the image light d with respect to themirror array 35. As a result, it is possible to suppress curvature ofimages formed in the imaging regions 41 a, 41 b . . . .

When the turning mirror 34 is divided into a plurality of mirrors, lightreflected by edge parts of the mirrors acts as stray light, and strikesthe mirror array 35 or enters the aperture stop portion 37. By using asingle plane mirror as the turning mirror 34 as in this embodiment, theeffect of stray light can be prevented even when both of the rays oflight overlap each other on the turning mirror 34. Although, in thisembodiment, the plane mirror 33 a is used to reduce the size of thereading module 50 in its height direction, it is also possible to adopta configuration where no plane mirror 33 a is used.

In a compound-eye reading method in which the mirror array 35 is used asin this embodiment, when the imaging magnification varies with theposition on a document (the optical path length between the reflectionmirrors and the document) within the region corresponding to thereflection mirrors 35 a, 34 b, 35 c . . . , when the document 60 floatsoff the contact glass 25, images overlap or separate from each other ata position next to border parts of the reflection mirrors 35 a, 35 b, 35c . . . , resulting in an abnormal image.

In this embodiment, a telecentric optical system is adopted where theimage light d is parallel to the optical axis from the document 60 tothe mirror array 35. The telecentric optical system has the feature thatthe principal ray of the image light d that passes through the center ofthe aperture stop portion 37 is perpendicular to the surface of thedocument. This prevents the imaging magnifications of the reflectionmirrors 35 a, 35 b, 35 c . . . from varying even when the documentposition varies; it is thus possible to obtain a reading module 50having a deep depth of field that does not cause image bleeding evenwhen the document 60 is read in a form divided into fine regions. Toachieve that, the principal ray needs to remain perpendicular to thesurface of the document irrespective of the document position, and thisrequires a mirror array 35 whose size in the main scanning direction isequal to or larger than the size of the document.

In the compound-eye reading method in which the mirror array 35 is usedas described above, when the image light d reflected from the reflectionmirrors 35 a, 35 b, 35 c . . . and transmitted through the aperture stopportion 37 is imaged in a predetermined region on the sensor 41, theimage light d traveling from outside the reading region, may, as straylight, strike a region next to the predetermined region on the sensor41.

FIG. 5 is a partly enlarged view showing the optical path between thereflection mirrors 35 a and 35 b and the sensor 41 in FIG. 4. As shownin FIG. 5, the light from the reading regions Ra and Rb corresponding tothe reflection mirrors 35 a and 35 b is imaged in the correspondingimaging regions 41 a and 41 b on the sensor 41. Here, the rays of light(indicated by hatched regions in FIG. 5) inward of the principal ray,even though they belong to the light traveling from outside the readingregions Ra and Rb, are imaged on the sensor 41 by the reflection mirrors35 a and 35 b. Specifically, the light reflected from the reflectionmirror 35 a strikes the adjacent imaging region 41 b, and the lightreflected from the reflection mirror 35 b strikes the adjacent imagingregion 41 a. These parts of the image light, even though feeble, forminverted images corresponding to different reading regions, and thus, ifsuperimposed on proper images which are supposed to be formed in theimaging regions 41 a and 41 b, produce abnormal images.

Thus, in this embodiment, the imaging magnifications of the reflectionmirrors 35 a, 35 b, 35 c . . . of the mirror array 35 are set to bereduction magnifications, and as shown in FIG. 6, light shielding walls43 are formed to protrude from the boundaries between the imagingregions 41 a and 41 b of the sensor 41 in the direction of the aperturestop portion 37.

Here, as shown in FIG. 6, for example, of the image light d which is tobe imaged in the imaging region 41 a on the sensor 41, the lighttraveling from outside the reading region Ra is shielded by the lightshielding wall 43; it is thus possible to prevent the stray light fromstriking the imaging region 41 b arranged next to the imaging region 41a in the main scanning direction. Here, assuming that the reflectionmirrors 35 a, 35 b, 35 c . . . are set at a unity magnification, thereflection mirrors 35 a, 35 b, 35 c . . . use the entire area over theimage forming regions 41 a, 41 b . . . up to their boundaries to formimages of the image light d. As a result, no space can be secured forforming the light shielding walls 43 at the boundaries of the imagingregions 41 a, 41 b . . . . To secure the space for forming the lightshielding walls 43, it is necessary to set the imaging magnifications ofthe reflection mirrors 35 a, 35 b, 35 c . . . to be reductionmagnifications as described above.

The optical unit 40 that includes the mirror array 35 and the aperturestop portion 37 preferably is, with consideration given to the cost,formed of resin by injection molding. Accordingly, it is necessary todetermine the reduction magnifications with a predetermined margin, withconsideration given to expansion or contraction due to change intemperature around the reading module 50 (hereinafter, referred to asenvironmental temperature). However, reducing the reductionmagnifications of the reflection mirrors 35 a, 35 b, 35 c . . .necessitates, when a sensor 41 with cell sizes (imaging regions)corresponding to the magnifications is used, a higher resolution on thesensor 41, and even when a sensor 41 with cell sizes for use in unitymagnification optical systems is used, a lower resolution results. Thus,it is preferable to maximize the reduction magnifications.

FIG. 7 is a partial perspective view showing the structure of theoptical unit 40 in the reading module 50 according to the firstembodiment. FIGS. 8 and 9 are perspective views of the aperture stopportion 37 used in the reading module 50 according to this embodiment asseen from the turning mirror 34 side (the left side in FIG. 2) and fromthe sensor 41 side (the right side in FIG. 2) respectively. As shown inFIG. 7, in the main scanning direction in which the reflection mirrors35 a, 35 b . . . of the mirror array 35 are continuously arranged, asmany aperture stop portions 37 as the number of the reflection mirrors35 a, 35 b . . . are continuously formed. FIGS. 8 and 9 show only oneunit (inside the broken-line circle in FIG. 7) of the aperture stopportion 37 corresponding to the reflection mirror 35 b. The otheraperture stop portions 37 corresponding to the reflection mirrors 35 a,35 c . . . have completely the same structure.

As shown in FIGS. 8 and 9, the aperture stop portion 37 has a firstaperture 37 a arranged on the sensor 41 side and a second aperture 37 barranged on the turning mirror 34 side (the mirror array 35 side). Thefirst aperture 37 a is a circular opening, and adjusts the amount of theimage light d which is to be imaged on the sensor 41. The secondaperture 37 b is a rectangular opening formed to communicate with thefirst aperture 37 a, and prevents part of the image light d reflectedfrom the adjacent reflection mirrors 35 a and 35 c from entering, asstray light, the first aperture 37 a. The first aperture 37 a and thesecond aperture 37 b are integrally formed of the same resin material.

By providing the aperture stop portion 37 with the first aperture 37 aand the second aperture 37 b as in this embodiment, it is possible toeffectively prevent the adverse effect of part of the image light dreflected from the adjacent reflection mirrors 35 a and 35 c passingthrough the first aperture 37 a corresponding to the reflection mirror35 b and striking, as stray light, a predetermined region on the sensor41. The aim of forming the opening of the second aperture 37 b in arectangular shape is to accurately separate from each other, with thestraight edges of the opening, the image light d from the reflectionmirror 35 b and the stray light from the adjacent reflection mirrors 35a and 35 c.

As described above, the second aperture 37 b corresponding to a givenreflection mirror (for example, the reflection mirror 35 b) is arrangedto prevent the stray light reflected from adjacent reflection mirrors(for example, the reflection mirrors 35 a and 35 c) and transmittedthrough the second aperture 37 b from directly entering the firstaperture 37 a. However, in this embodiment, the first aperture 37 a andthe second aperture 37 b are integrally formed as one structural member,and thus the stray light which passes through the second aperture 37 bbut does not directly enter the first aperture 37 a may be reflected onthe inner wall surface present between the first aperture 37 a and thesecond aperture 37 b, pass through the first aperture 37 a, and strikethe sensor 41. Accordingly, it is necessary to reduce reflection oflight between the first aperture 37 a and the second aperture 37 b, andthereby to prevent the stray light from striking the sensor 41.

FIG. 10 is a perspective view of the aperture stop portion 37 used inthe reading module 50 according to this embodiment as seen from above.FIG. 10 shows a state with the top surface removed to expose the insideof the aperture stop portion 37.

As shown in FIG. 10, the aperture stop portion 37 has first apertures 37a formed in a sensor 41-side (the upper right side in FIG. 10) wallportion 38 a of an aperture stop main body 38 in the shape of a hollowrectangular parallelepiped. In a turning mirror 34-side (the lower leftside in FIG. 10) wall portion 38 b of the aperture stop main body 38,second apertures 37 b are formed at positions facing the first apertures37 a respectively. The interior of the aperture stop main body 38 isdivided into a plurality of spaces S by partition walls 38 d formedbetween every two adjacent ones of the first apertures 37 a and thesecond apertures 37 b. With this configuration, each pair of first andsecond apertures 37 a and 37 b facing each other are arranged oppositeeach other across the spaces S. The spaces S constitute a reflectionreduction mechanism that reduces reflection of light in the direction ofthe first aperture 37 a other than image light traveling from the secondaperture 37 b to the first aperture 37 a.

FIG. 11 is a diagram schematically showing how stray light F enters theaperture stop portion 37 used in the reading module 50 according to thisembodiment. The stray light F is light which passes through the secondaperture 37 b but does not directly enter the aperture 37 a, that is,light other than image light which enters the aperture stop main body 38through the second aperture 37 b. As shown in FIG. 11, the stray light Fhaving entered the aperture stop main body 38 through the secondaperture 37 b attenuates as it travels through the space S while beingreflected on the partition walls 38 d and the wall portions 38 a and 38b. Thus, it is possible to suppress the phenomenon in which stray lightF which passes through the second aperture 37 b but does not directlyenter the first aperture 37 a is reflected to enter the first aperture37 a.

FIG. 12 is a perspective view of an aperture stop portion 37 used in areading module 50 according to a second embodiment of the presentdisclosure as seen from above. FIG. 13 is a diagram schematicallyshowing how stray light F enters the aperture stop portion 37 used inthe reading module 50 according to this embodiment. Like FIG. 10, FIG.12 shows a state with the top surface removed to expose the inside ofthe aperture stop portion 37. In this embodiment, there are providedribs 70 which protrude into the spaces S from the partition walls 38 dand wall portions 38 c parallel to the partition walls 38 d. The spacesS and the ribs 70 constitute a reflection reduction mechanism thatreduces reflection of light in the direction of the first aperture 37 aother than image light traveling from the second aperture 37 b to thefirst aperture 37 a. Otherwise, the structure of the aperture stopportion 37 is similar to that in the first embodiment.

As shown in FIGS. 12 and 13, two ribs 70 are formed on each of mutuallyfacing ones of the partition walls 38 d and the wall portions 38 c. Eachpair of ribs 70 located opposite each other is formed in line symmetrywith respect to an image light passage region R1 (the region presentbetween dotted lines in FIG. 13) through which image light passes fromthe second aperture 37 b to the first aperture 37 a. The ribs 70 areinclined in a direction approaching the image light passage region R1from the second aperture 37 b side to the first aperture 37 a side.

As shown in FIG. 13, the stray light F having entered the aperture stopmain body 38 through the second aperture 37 b is reflected from the rib70 and emerges from the second aperture 37 b again toward the turningmirror 34 (see FIG. 3) or attenuates as it travels through the space Swhile being reflected on another rib 70 located opposite across theimage light passage region R1, on the partition walls 38 d, on the wallportions 38 b and 38 c, and the like. Thus, as in the first embodiment,it is possible to suppress the phenomenon in which stray light F whichpasses through the second aperture 37 b but does not directly enter thefirst aperture 37 a is reflected to enter the first aperture 37 a.

FIG. 14 is a sectional plan view showing the structure between onereflection mirror 35 b and the sensor 41 in the reading module 50according to this embodiment. The structures between other reflectionmirrors 35 a, 35 c . . . and the sensor 41 are similar to that shown inFIG. 14. For the sake of convenience of description, like FIG. 4, FIG.14 shows a model where the optical unit 40 transmits rays of light. InFIG. 14, for the sake of convenience of description, the second aperture37 b is omitted from illustration, and only one of the plurality of ribs70 is illustrated. With reference to FIG. 14, a description will begiven of how the range of the inclination angle α of the rib 70 relativeto the main scanning direction is determined.

Now, the center of the sensor 41 in the main scanning direction is takenas the coordinate origin O, the straight line that, starting at thecoordinate origin O, runs parallel to the sensor 41 (in the mainscanning direction) is taken as the X-axis, and the straight line that,starting at the coordinate origin O, runs perpendicular to thereflection mirror 35 b is taken as the Y-axis. Here, the mirror width ofthe reflection mirror 35 b in the main scanning direction is representedby a, the distance (distance in the Y-axis direction) from the firstaperture 37 a to the base end part of the rib 70 is represented by h,and the distances from the first aperture 37 a to the reflection mirror35 b and to the sensor 41 are represented by z and z′ respectively.

Rays of light D1 are incident light from the mirror array 35 reflectedat point E on the reflection mirror 35 b and forming an angle of θdegrees relative to the X-axis, and an arrow indicates the travelingdirection of the rays of light. Let the coordinates of point E be (d,z+z′); then the rays of light D1 are expressed by the formula below.y=tan θ×x+z+z′−d tan θ  (1)

Here, the x coordinate d of point E is within the range of 0≤d≤a/2. Theangle θ of the rays of light D1 relative to the X-axis is larger thanthe inclination angle α of the rib 70, and thus 0≤α<θ, that is, 0≤tanα<tan θ. Let the coordinates of point F of the base end part of the rib70 be (a/2, z′+h); then the rib 70 is expressed by the formula below.y=tan α×x+z′+h−a/2×tan α  (2)

The rays of light D2 are reflected light of the rays of light D1 withrespect to the rib 70, and an arrow indicates the traveling direction ofthe rays of light. That is, the rays of light D2 are in line symmetrywith the rays of light D1 with respect to the normal line L to the rib70. Here, the rays of light D2 are expressed by the formula below.Y=−{(tan θ tan² α+2 tan α−tan θ)/(tan² α−2 tan θ tanα−1)}×x−{(tan²α+1)(h−z−a/2 tan α+d tan θ)}/(tan² α−2 tan θ tanα−1)+z′+h−a/2×tan α  (3)Here, to prevent the rays of light D2 from reaching the sensor 41, theformula below needs to be fulfilled.−(tan θ tan² α+2 tan α−tan θ)/(tan² α−2 tan θ tan α−1)<0  (4)

Consider the sign of tan² α−2 tan θ tan α−1, which is the denominator ofinequality (4). Seeing that tan² α−2 tan θ tan α−1=(tan α−tan θ)²−1−tan²θ and that, as mentioned above, tan α<tan θ, (tan α−tan θ)²−1−tan²θ<(tan θ−tan θ)²−1−tan² θ=−1−tan² θ<0.

Based on what is described above, to fulfill inequality (4), it isnecessary that −(tan θ tan² α+2 tan α−tan θ)>0 be fulfilled, that is,tan θ tan² α+2 tan α−tan θ<0 be fulfilled. This can be considered aquadratic inequality with respect to tan α, and solving it with respectto tan α with consideration given to 0≤tan α<tan θ gives the inequalitybelow.0≤tan α<{−1+√(1+tan² θ)}/tan θ  (5)Accordingly, when the inclination angle α of the rib 70 is set such thatit fulfills inequality (5) above, the rays of light D2 do not reach thesensor 41.

FIG. 15 is a perspective view of an aperture stop portion 37 used in areading module 50 according to a third embodiment of the presentdisclosure as seen from the turning mirror 34 side (the left side inFIG. 2). FIG. 16 is an enlarged view of the aperture stop portion 37 inFIG. 15 as seen from the second aperture 37 b side. Like FIGS. 8 and 9,FIGS. 15 and 16 show only one unit (inside the broken-line circle inFIG. 7) of the aperture stop portion 37 corresponding to one of thereflection mirrors 35 a, 35 b, 35 c . . . . FIGS. 15 and 16 show onlythe bottom half of the aperture stop portion 37 with the top half of itremoved.

In this embodiment, the image light passage region R1 through whichimage light passes from the second aperture 37 b to the first aperture37 a is surrounded by inner wall surfaces 37 c from four, i.e., up,down, left and right, sides (FIG. 15 showing only inner wall surfaces 37c at three, i.e., left, right, and down, sides). The inner wall surfaces37 c are coarse surfaces treated by texturing, and as shown in FIG. 16,fine irregularities 71 are formed over the entire area of the inner wallsurfaces 37 c. The light having entered through the second aperture 37 bis reflected on the inner wall surfaces 37 c to become scattered lightscattered in irregular directions. The irregularities 71 constitute areflection reduction mechanism that reduces reflection of light in thedirection of the first aperture 37 a other than image light travelingfrom the second aperture 37 b to the first aperture 37 a.

Thus, as in the first and second embodiments, it is possible to suppressthe phenomenon in which stray light F which passes through the secondaperture 37 b but does not directly enter the first aperture 37 a isreflected on the inner wall surfaces 37 c to enter the first aperture 37a.

FIG. 17 is a perspective view of an aperture stop portion 37 used in areading module 50 according to a fourth embodiment of the presentdisclosure as seen from the turning mirror 34 side (the left side inFIG. 2). FIG. 18 is a perspective view of the aperture stop portion 37used in the reading module 50 according to the fourth embodiment of thepresent disclosure as seen from the sensor 41 side (the right side inFIG. 2). FIG. 19 is a sectional view across line 200-200 in FIG. 17.FIG. 20 is a diagram schematically showing how light is reflected oninner surfaces 37 e of the second aperture 37 b of the aperture stopportion 37 used in the reading module 50 according to the fourthembodiment of the present disclosure. Like FIGS. 8 and 9, FIGS. 17 to 20show only one unit (inside the broken-line circle in FIG. 7) of theaperture stop portion 37 corresponding to one of the reflection mirrors35 a, 35 b, 35 c . . . . FIGS. 17 to 20 show a state with the topsurface removed to expose the inside of the aperture stop portion 37.

In this embodiment, the aperture stop main body 38 has inclined surfaces37 d inclined with respect to the main scanning direction as seen fromthe direction of the optical axis (the direction from the secondaperture 37 b to the first aperture 37 a). The inclined surfaces 37 dare arranged opposite each other in the main scanning direction acrossthe image light passage region R1 through which image light passes. Thespace S and the inclined surfaces 37 d constitute a reflection reductionmechanism that reduces reflection of light in the direction of the firstaperture 37 a other than image light traveling from the second aperture37 b to the first aperture 37 a.

The inclined surfaces 37 d are inclined with respect to the mainscanning direction by the inclination angle θ 37 d (see FIG. 19). Theinclination angle θ 37 d is preferably equal to or larger than 40° butequal to or smaller than 65°. To prevent the stray light F reflected onthe inclined surfaces 37 d from traveling toward the first aperture 37 awithout increasing the length of the inclined surfaces 37 d in the mainscanning direction, it is preferable that the inclination angle θ 37 dbe equal to or larger than 55° but equal to or smaller than 60°, andhere it is set at about 60°.

The stray light F having entered the aperture stop main body 38 throughthe second aperture 37 b is reflected by the inclined surface 37 dupward, above the first aperture 37 a, and attenuates as it isrepeatedly reflected on the wall portions 38 a and 38 b, on the inclinedsurfaces 37 d, and the like. Thus, as in the first to third embodiments,it is possible to suppress the phenomenon in which stray light F whichpasses through the second aperture 37 b but does not directly enter thefirst aperture 37 a is reflected to enter the first aperture 37 a.

In this embodiment, the second aperture 37 b is a rectangular openingformed to communicate with the first aperture 37 a, and the innersurfaces 37 e of the second aperture 37 b arranged opposite each otherin the main scanning direction are inclined in a direction approachingthe image light passage region R1 toward the first aperture 37 a. Whenthe inclination angle θ 37 e (see FIG. 20) of the inner surfaces 37 e ofthe second aperture 37 b with respect to the main scanning direction isset, for example, equal to or smaller than 45°, it is possible to almostcompletely prevent the light (indicated by broken-line arrows in FIG.20) reflected from the inner surface 37 e from entering the aperturestop main body 38.

In this embodiment, the first aperture 37 a is a circular opening, andan inner circumferential surface 37 f of the first aperture 37 a isformed in a tapered shape to be increasingly wide toward the sensor 41.Specifically, the inner circumferential surface 37 f is formed to beincreasingly wide toward the sensor 41 at 2° or more (here about 2.5°).In plan view, a sensor 41-side (the upper side in FIG. 20) edge 37 g ofthe inner circumferential surface 37 f is preferably arranged outward ofa straight line L37 in the main scanning direction which connectstogether a turning mirror 34-side (the lower side in FIG. 20) edge 37 hof the inner circumferential surface 37 f and a sensor 41-side (theupper side in FIG. 20) edge 37 i of the inner surface 37 e of the secondaperture 37 b. With this configuration, it is possible to prevent straylight F from being reflected on the inner circumferential surface 37 fof the first aperture 37 a to strike the sensor 41.

The embodiments described above are in no way meant to limit the presentdisclosure, which thus allows for many modifications and variationswithin the spirit of the present disclosure. For example, although inthe above-described embodiments, image light d which travels from thedocument 60 via the plane mirror 33 a to strike the mirror array 35 andimage light d which is reflected from the mirror array 35 to enter theaperture stop portion 37 are each reflected on the turning mirror 34once, that is, reflection on it takes place twice in total, as shown inFIG. 21, with a plane mirror 33 b arranged on the optical unit 40 side,image light d may be reflected on the turning mirror 34 three times ormore.

Although the above-described embodiments deal with, as an example of animage reading device, the image reading portion 6 incorporated in theimage forming apparatus 100, the present disclosure is applicableequally to an image scanner used separately from the image formingapparatus 100.

For example, the fourth embodiment deals with an example where theaperture stop portion 37 has the inclined surfaces 37 d, the innersurfaces 37 e of the second aperture 37 b are inclined with respect tothe main scanning direction, and the inner circumferential surface 37 fof the first aperture 37 a is formed to be increasingly wide toward thesensor 41; however, this is in no way meant to limit the presentdisclosure. For example, in the previously-described first and secondembodiments, the inner surfaces 37 e of the second aperture 37 b may beinclined with respect to the main scanning direction. For anotherexample, in the previously-described first to third embodiments, theinner circumferential surface 37 f of the first aperture 37 a may beformed to be increasingly wide toward the sensor 41.

The technical scope of the present disclosure encompasses any structureobtained by combining together different features from theabove-described embodiments and modified examples as necessary.

The present disclosure is applicable to image reading devices providedwith a reading module adopting a reading configuration includingreflection mirrors arranged in an array. Based on the presentdisclosure, it is possible to provide an image reading device that can,with a simple configuration, prevent stray light from striking a sensorin which sensor chips corresponding to the reduction magnifications ofreflection mirrors are arranged next to each other on a base substrate,and to provide an image forming apparatus provided with such an imagereading device.

What is claimed is:
 1. A reading module comprising: a light source whichradiates light to a document; an optical system which images, as imagelight, reflected light of the light radiated from the light source tothe document; and a sensor in which a plurality of imaging regions forconverting the image light imaged by the optical system into anelectrical signal are arranged next to each other in a main scanningdirection, wherein the optical system comprises: a mirror array in whicha plurality of reflection mirrors whose reflection surfaces areaspherical concave surfaces are coupled together in an array in the mainscanning direction; and a plurality of aperture stop portions eachprovided in an optical path of the image light between a reflectionmirror and an imaging region of the sensor, the plurality of aperturestop portions each having: a first aperture which adjusts an amount ofthe image light reflected from the reflection mirror; and a secondaperture formed on a mirror array side of the first aperture, the secondaperture shielding stray light that enters the first aperture from anadjacent reflection mirror, and between the first aperture and thesecond aperture, a reflection reduction mechanism is provided thatreduces reflection, toward the first aperture, of light other than theimage light traveling from the second aperture to the first aperture. 2.The reading module of claim 1, wherein the first aperture and the secondaperture are openings provided in an aperture stop main body on a sensorside and on the mirror array side thereof respectively.
 3. The readingmodule of claim 2, wherein the reflection reduction mechanism is a spaceformed between the first aperture and the second aperture in theaperture stop main body.
 4. The reading module of claim 3, wherein inthe aperture stop main body, a rib is formed to protrude from an innerwall surface perpendicular to the first aperture and the second apertureinto the space toward a region through which the image light passes, andthe rib is inclined in a direction approaching the region from thesecond aperture to the first aperture.
 5. The reading module of claim 4,wherein let an angle, with respect to the main scanning direction, oflight traveling from the reflection mirror to enter the second aperturebe θ, then an inclination angle α of the rib with respect to the mainscanning direction fulfills a formula below,0≤tan α<{−1+√(1+tan² θ)}/tan θ.
 6. The reading module of claim 3,wherein in the aperture stop main body, inclined surfaces are providedwhich are arranged opposite each other in the main scanning directionacross a region through which the image light passes, the inclinedsurfaces being inclined with respect to the main scanning direction asseen from a direction of an optical axis.
 7. The reading module of claim2, wherein the reflection reduction mechanism is irregularities formedon an inner wall surface perpendicular to the first aperture and thesecond aperture in the aperture stop main body.
 8. The reading module ofclaim 2, wherein the second aperture is a rectangular opening, and innersurfaces of the second aperture arranged opposite each other in the mainscanning direction are inclined in a direction approaching the regiontoward the first aperture.
 9. The reading module of claim 2, wherein thefirst aperture is a circular opening, and an inner circumferentialsurface of the first aperture is formed to be increasingly wide towardthe sensor.
 10. The reading module of claim 1, wherein the opticalsystem is a telecentric optical system where the image light is parallelto an optical axis on a document side of the mirror array, and forms aninverted image on the sensor.
 11. The reading module of claim 10,wherein imaging magnifications of the reflection mirrors for therespective imaging regions are set at reduction magnifications, and alight shielding wall is provided which is formed to protrude from aboundary between adjacent imaging regions toward the aperture stopportions, the light shielding wall shielding stray light which is to beincident on the imaging regions.
 12. The reading module of claim 11,wherein image data read in the imaging regions of the sensor undergoesmagnification enlargement correction through data interpolationaccording to the reduction magnifications to reverse the data into erectimages, and then the images in the imaging regions are connectedtogether to form a read image corresponding to the document.
 13. Thereading module of claim 1, wherein an optical path of the image lighttraveling toward each reflection mirror and an optical path of the imagelight traveling toward an aperture stop portion run in a same direction,a turning mirror which bends the image light reflected from thereflection mirror toward the aperture stop portion is arranged at aposition facing the mirror array, and the turning mirror bends the imagelight twice or more times on a same reflection surface thereof,including bending the image light traveling toward the reflection mirrorand bending the image light reflected from the reflection mirror towardthe aperture stop portion.
 14. An image reading device, comprising: acontact glass fixed to a top surface of an image reading portion; adocument conveyance device which is openable/closable upward withrespect to the contact glass, the document conveyance device conveying adocument to an image reading position of the contact glass; and thereading module of claim 1 arranged to be reciprocable under the contactglass in a sub-scanning direction, wherein the reading module is capableof reading an image of a document placed on the contact glass whilemoving in the sub-scanning direction, and the reading module is capableof reading an image of a document conveyed to the image reading positionwhile remaining at rest at the position facing the image readingposition.
 15. An image forming apparatus comprising the image readingdevice of claim 14.